1. Field of the Invention
The present invention relates to an electroluminescent device, more specifically to an electroluminescent device consisting of organic compounds as emitter.
2. Description of the Prior Art
As such type of electroluminescent devices, there have been known a two-layer structure, as is shown in FIG. 1, in which an organic fluorescent film 3 and an organic positive-hole transporting layer 4 are arranged between a metal electrode 1 as cathode and a transparent electrode 2 as anode, the two layers both comprising organic compounds and being layered on each other, and a three-layer structure, as is shown in FIG. 2, in which an organic electron transporting layer 5, an organic fluorescent film 3 and an organic positive-hole transporting layer 4, are arranged between a metal electrode 1 and a transparent electrode 2. The organic positive-hole transporting layer 4 herein has a function to facilitate the injection of positive holes from an anode as well as another function to block electrons, while the organic electron transporting layer 5 has a function to facilitate the injection of electrons from a cathode.
In these electroluminescent devices where a glass substrate 6 is arranged outside the transparent electrode 2, excitons are generated from the recombination of the electrons injected from the metal electrode 1 with the positive holes injected to the organic fluorescent film 3 from the transparent electrode 2. At the stage where the excitons are inactivated through radiation, they emit light which is then emitted toward outside through the transparent electrode 2 and the glass substrate 6.
As is disclosed in the Japanese Patent Laid-open No. 264692/1988, there have been also known stably emitting electroluminescent devices comprising a fluorescent film formed from an organic host material and a fluorescent guest material. Although the conventional electroluminescent devices with such aforementioned composition comprising organic compounds, can emit light at a lower voltage, there is a desire toward electroluminescent devices capable of emission at a high luminance.